Content presented for viewing by a user may include items or objects that are within the view of the user. For example, a single screen on an electronic display may include one or more text items, and one or more images. Though all of such items may be presented for viewing, there may be a desire to know whether the viewer actually viewed such items, which ones were viewed and for how long. As the eyes of the viewer are complex organs that move in a very specific way, where the pupil is a hole located in the center of the iris of the eye that allows light to strike the retina, locating the exact point of the gaze of the viewer is difficult to accomplish.
Further, various physical maladies and indications may be accompanied by or result in changes or variations in the capacity of a viewer to track, view, or follow an item in the field of view of the viewer.